In short, how many arguments does the verb take? Sometimes it can be tricky because a verb can have multiple argument configurations. (Check your textbook for whether you're supposed to classify it twice, or classify it based on the most possible arguments, or something else.)

The problem is my text book just gives me this patterns:-intransitive: (S+V)-monotransitive: (S+V+DO)-copular: (S+V+SP) and (S+V+A)-ditransitive: (S+V+IO+DO)-complex transitive (S+V+DO+OP) and (S+V+DO+A).

Verbs themselves only form the verb phrase. More complex sentences have other phrases doing other things. Or potentially other things (non-arguments) in the verb phrase like adverbs. "I walk" and "I walk frequently" use the same verb, which is intransitive in both cases, even though there's an additional adverb in the second phrase.

What I do is that I check what is after the verb, in this way I can identify if the verb is transitive, intransitive, ditransitive, intensive, or complex. I assume that when you are talking about more complex sentences you are talking about subordinate clauses, I think my advise still applies in this case.